Private bus operators on Saturday worked out a proposal for converting old vehicles to conform to Bharat Stage II norms.

The move follows a Calcutta High Court directive that a new method be adopted to improve the engines of old vehicles. “All vehicles will have to conform to Bharat Stage II norms. The changeover will have to be done within a year,” the court said.

For the conversion, owners of all diesel-run vehicles, more than 12 years old, will either have to install a new engine or switch to other eco-friendly fuels. This has posed a problem for transport operators as the switchover involves time and money.

According to the proposal, diesel-run vehicles will be fitted with five devices — catalytic converter, exhaust gas recycling system, steam injection system, nozzle injection and fuel pump calibration — to maintain the mass emission standard, while the engines will remain unchanged.

“After conducting tests in the pollution control board laboratory and Jadavpur University, we found that old vehicles containing the five devices conform to the Bharat Stage II norms. We will start installing the devices as soon as we get the nod from the transport department,’’ said an automobile expert. The package will cost around Rs 15,000.

Dipen Banerjee, secretary of Passenger Transport and Service Committee, said they had no option but to install the devices as most bus operators were not in a position to fit a new engine costing nearly Rs 3 lakh.